The board said in a statement on Monday the company's shares are worth "considerably more" than the current book value, and that a buyback would boost Berkshire's shares to better represent their "intrinsic" value.

The plan was left flexible to timing, duration and amount to be spent on the buyback, with the only limitation being ensuring the company's cash holdings do not drop below $US20 billion ($20.43 billion).

At mid-year the company reported nearly $US48 billion in cash.

"The repurchase program is expected to continue indefinitely and the amount of purchases will depend entirely upon the levels of cash available, the attractiveness of investment and business opportunities either at hand or on the horizon, and the degree of discount from management's estimate of intrinsic value," a company statement said.

Berkshire has a sprawling portfolio of investments in insurance, utilities, banking, transportation, manufacturing, consumer goods and services industries, some of which it runs and some as a passive investor.

Berkshire's A shares, the most costly listed shares in the United States, were up 5.3 per cent to $US105,659.99 in early trade following the announcement.